Powder metallurgy wear and corrosion resistance alloy

ABSTRACT

A powder metallurgy wear and corrosion resistance alloy includes chemical components by mass percent of: C: 2.36%-3.30%, W: 0.1%-1.0%, Mo: ≤1.8%, Cr: 12.6%-18.0%, V: 6.0%-12.5%, Nb: 0.5%-2.1%, Co: 0.1%-0.5%, Si: ≤1.0%, Mn: 0.2%-1.0%, N: 0.05%-0.35%, with balance iron and impurities; wherein a carbide component of the powder metallurgy wear and corrosion resistance alloy is an MX carbide and a M 7 C 3  carbide, wherein the MX carbide has a NaCl type face-centered cubic lattice structure; an M element of the MX carbide comprises V and Nb, and an X element of the MX carbide comprises C and N.

CROSS REFERENCE OF RELATED APPLICATION

This is a U.S. National Stage under 35 U.S.C 371 of the InternationalApplication PCT/CN2015/091274, filed on Sep. 30, 2015, which claimspriority under 35 U.S.C. 119(a-d) to CN 201510248007.X, filed on May 15,2015.

BACKGROUND OF THE PRESENT INVENTION Field of Invention

The present invention relates to a tool steel alloy, and moreparticularly to a powder metallurgy wear and corrosion resistance alloy.

Description of Related Arts

In some special working conditions, tools or parts are worn due todirect contact with hard abrasive particles of moving parts or workingmediums, while corroded by moisture, corrosive acids or other corrosiveagents. Under such typical operating conditions, parts such as screw,screw head and screw sleeve used in plastic injection molding machineare fiercely worn due to a lot of hard grains such as glass fibers andcarbon fibers added in the plastic; while being chemically corroded bycorrosion components in the plastic. For obtaining a long part servicelife under such special conditions, a tool steel used must have highwear resistance and corrosion resistance. In addition, to bear loadingand shock of working stress, the tool steel needs certain hardness andtoughness. Wear resistance of the tool steel depends on the matrixhardness, as well as content, morphology and particle size distributionof the second hard phase in the steel. The second hard phase in thesteel comprises M₆C, M₂C, M₂₃C₆, M₇C₃ and MX carbides, whereinmicrohardness of the MX carbides are higher than other carbides, forproviding better matrix protection during operation, thereby reducingwear and improving the service life of molds. Corrosion resistanceincrease of the tool steel mainly depends on chromium dissolved in thematrix, and it is considered that 11% chromium should be dissolved inthe matrix. Toughness of the tool steel depends on the matrix hardnessand particle size distribution of the second hard phase in the steel.Coarse carbides in the steel will cause stress concentration, whichreduces the toughness of the tool steel, resulting in fracture under arelatively low external load. In order to improve the toughness of thetool steel, it is important to reduce or refine the carbides. In orderto avoid plastic deformation during utilization, hardness of the toolsteel is usually required to be HRC60 or more.

Conventionally, the tool steel is mainly casted and forged bytraditional production processes, wherein the tool steel prepared bycasting and forging processes is limited by liquid steel which is slowlycooled during the processes. As a result, alloy components are easy tobe segregated during consolidation and to form the coarse carbides. Evenafter subsequent forging and rolling processes, such bad structure willstill adversely affect the performance of the alloy, resulting in lowperformances of the tool steal in strength, toughness, wear resistanceand grinding performance, which is difficult to meet materialperformance and life stability requirements of high-end manufacturing.Tool steel prepared by a powder metallurgy method avoids the segregationproblem of alloy elements, wherein the powder metallurgy methodcomprises steps of: preparing powder by atomization, and consolidatingthe powder. In the step of preparing powder by atomization, the liquidsteel is rapidly cooled into powder. Therefore, the alloy elements inthe liquid steel are completely consolidated before segregation. Astructure is fine and even after powder consolidation, wherein comparedwith casting and forging, alloy performance is significantly improved.Conventionally, only the powder metallurgy method is able to satisfyextremely high performance requirements of high alloy tool steel. Toolsteel prepared by powder metallurgy has been reported, but components ofsome kinds of steel are not reasonably designed, so structure andperformance should be further improved.

SUMMARY OF THE PRESENT INVENTION

An object of the present invention is to solve at least one of the abovetechnical problems to some extent. Therefore, the present inventionprovides a powder metallurgy wear and corrosion resistance alloy withexcellent performances.

Accordingly, in order to accomplish the above objects, the presentinvention provides a powder metallurgy wear and corrosion resistancealloy, comprising chemical components by mass percent of: C:2.36%-3.30%, W: 0.1%-1.0%, Mo: ≤1.8%, Cr: 12.6%-18.0%, V: 6.0%-12.5%,Nb: 0.5%-2.1%, Co: 0.1%-0.5%, Si: ≤1.0%, Mn: 0.2%-1.0%, N: 0.05%-0.35%,with balance iron and impurities; wherein a carbide component of thepowder metallurgy wear and corrosion resistance alloy is an MX carbideand a M₇C₃ carbide, wherein the MX carbide has a NaCl type face-centeredcubic lattice structure; an M element of the MX carbide comprises V andNb, and an X element of the MX carbide comprises C and N.

According to the powder metallurgy wear and corrosion resistance alloyof an embodiment of the present invention, alloy components are designedand powder metallurgy is adapted, for obtaining an alloy with high wearresistance and high corrosion resistance. According to the presentinvention, the MX carbide comprises alloy elements such as C, N, V andNb. A type of the MX carbide is (V, Nb) (C, N). Under a rapid coolingcondition of liquid steel, Nb and N are involved in formation of the MXcarbide, so as to increase a nucleation rate and refine the MX carbide,in such a manner that toughness of the alloy is improved.

Preferably, the impurities comprise O, wherein an O content is no morethan 0.01%.

Preferably, the powder metallurgy wear and corrosion resistance alloycomprises the chemical components by mass percent of: C: 2.40%-3.18%, W:0.1%-0.8%, Mo: ≤1.8%, Cr: 13.0%-18.0%, V: 6.2%-12.5%, Nb: 1.0%-2.0%, Co:0.1%-0.4%, Si: ≤0.8%, Mn: 0.2%-0.8%, N: 0.05%-0.30%, O: ≤0.008%, withbalance iron and impurities.

Preferably, the impurities comprise S, wherein a S content is no morethan 0.1%.

Preferably, the impurities comprise P, wherein a P content is no morethan 0.03%.

Preferably, a volume fraction of the MX carbide is 12%-20%.

Preferably, a size of at least 80% of the MX carbide is no more than 1.3μm judging from volume percentage.

Preferably, a maximum size of the MX carbide is no more than 5.0 μm.

Preferably, the M₇C₃ carbide is a Cr-enriched carbide.

Preferably, a volume fraction of the M₇C₃ carbide is 12%-19%.

Preferably, a size of at least 80% of the M₇C₃ carbide is no more than 5μm judging from volume percentage.

Preferably, a maximum size of the M₇C₃ carbide is no more than 10 μm.

Preferably, the M₇C₃ carbide has a hexagonal lattice structure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Preferred embodiments of the present invention are illustrated asfollows. Examples of the embodiments are shown in drawings. The same orsimilar elements and the elements having same or similar functions aredenoted by like reference numerals throughout the descriptions. Theembodiments described herein with reference to drawings are explanatory,and used to generally understand the present disclosure, and notintended to be limiting.

The present invention provides a powder metallurgy wear and corrosionresistance alloy with significant performances. According to the presentinvention, the powder metallurgy wear and corrosion resistance alloycomprises chemical components by mass percent of: C: 2.36%-3.30%, W:0.1%-1.0%, Mo: ≤1.8%, Cr: 12.6%-18.0%, V: 6.0%-12.5%, Nb: 0.5%-2.1%, Co:0.1%-0.5%, Si: ≤1.0%, Mn: 0.2%-1.0%, N: 0.05%-0.35%, with balance ironand impurities; wherein a carbide component of the powder metallurgywear and corrosion resistance alloy is an MX carbide and a M₇C₃ carbide,wherein the MX carbide has a NaCl type face-centered cubic latticestructure; an M element of the MX carbide comprises V and Nb, and an Xelement comprises C and N.

According to the embodiments of the present invention, alloy componentsare designed and powder metallurgy is adapted, for obtaining an alloywith high wear resistance and high corrosion resistance.

C is dissolved in the matrix for enhancing matrix strength. Meanwhile, Cis one of forming elements of carbide, whose content should be no lessthan 2.36%, so as to ensure that the alloy elements are fully involvedin carbide precipitation. A maximum C content is no more than 3.30%, foravoiding toughness decrease due to excessive C dissolved in the matrix.A C content is at 2.36%-3.30% for optimizing a combination of wearresistance and toughness.

W and Mo are dissolved in the matrix for increasing hardenabilitythereof. According to the present invention, a W content is 0.1%-1.0%,and a Mo content is Mo≤1.8%.

On one hand, Cr is dissolved in the matrix for improving corrosionresistance and hardenability thereof; on the other hand, Cr isprecipitated as the M₇C₃ carbide. In consideration of a balance betweenCr dissolved in the matrix and precipitated as carbide, a Cr content ofthe present invention is 12.6%-18.0%.

V is used for forming the MX carbide and improving alloy wearresistance, whose content is controlled between 6.0%-12.5%.

Nb and V have similar functions, both of which are involved in formingthe MX carbide. According to the present invention, Nb is dissolved inthe MX carbide for increasing a nucleation rate when the MX carbide isprecipitated, so as to improve precipitating and refining of the MXcarbide, and improve the wear resistance. A Nb adding limit preventsNb-enriched MX carbide from precipitation. According to the presentinvention, a Nb content is controlled at 0.5%-2.1%.

Co is mainly dissolved in the matrix for promoting carbide precipitationand refining particle size of the carbide. According to the presentinvention, a Co content is 0.1%-0.5%.

Si is not involved in carbide formation, but as a deoxidizing agent anda strengthening element of the matrix. Excessive Si will lower thetoughness of the matrix, so a Si content is controlled at Si≤1.0%.

Mn is added as a deoxidizing agent, for fixing sulfur and reducing hotbrittleness. In addition, manganese increases a hardenability. Accordingto the present invention, a Mn content is controlled within 0.2%-1.0%.

N is involved in MX carbide formation. Under a rapid cooling condition,N promotes nucleation precipitation of the MX carbide while the MXcarbide never excessively grows, which is conducive to improvement ofthe wear resistance as well as corrosion resistance. A N content islimited within 0.05%-0.35%.

According to the embodiments of the present invention, the MX carbidecomprises alloy elements such as C, N, V and Nb. A type of the MXcarbide comprises (V, Nb) (C, N). Under a rapid cooling condition ofliquid steel, Nb and N are involved in formation of the MX carbide, soas to increase a nucleation rate and refine the MX carbide, in such amanner that toughness of the alloy is improved.

Preferably, the impurities comprise O, wherein an O content is no morethan 0.01%.

Excessive O will lower the toughness of the alloy. According to theembodiments of the present invention, the O content is no more than0.01% for ensuring an outstanding steel performance.

Preferably, the powder metallurgy wear and corrosion resistance alloycomprises the chemical components by mass percent of: C: 2.40%-3.18%, W:0.1%-0.8%, Mo: ≤1.8%, Cr: 13.0%-18.0%, V: 6.2%-12.5%, Nb: 1.0%-2.0%, Co:0.1%-0.4%, Si: ≤0.8%, Mn: 0.2%-0.8%, N: 0.05%-0.30%, O: ≤0.008%, withbalance iron and impurities.

For obtaining a better combination performance, the chemical componentsof the powder metallurgy wear and corrosion resistance alloy should becontrolled within a certain range.

Preferably, a volume fraction of the MX carbide is 12%-20%.

Preferably, a size of at least 80% of the MX carbide is no more than 1.3μm judging from volume percentage, and a maximum size of the MX carbideis no more than 5 μm.

Preferably, the M₇C₃ carbide has a complex hexagonal lattice structure,a main element M in the M₇C₃ carbide is Cr.

Preferably, a volume fraction of the M₇C₃ carbide is 12%-19%.

Preferably, a size of at least 80% of the M₇C₃ carbide is no more than 5μm judging from volume percentage, and a maximum size of the M₇C₃carbide is no more than 10 μm.

According to the embodiments of the present invention, the powdermetallurgy wear and corrosion resistance alloy is prepared by a methodcomprising steps of:

a) preparing a liquid tool steal with the above components and loadingthe liquid tool steal into a ladle;

b) electrically heating covering slag at a top surface of the liquidsteel in the ladle for maintaining superheat, injecting an inert gasfrom a hole at a bottom of the ladle for stirring the liquid steel;

c) moving the liquid steel into a tundish which is pre-heated throughthe guiding tube at the bottom of the ladle, adding covering slag to thetop surface of the liquid steel when the liquid steel enters into thetundish and buries a bottom end face of the guiding tube;

d) continuously additional heating the tundish for maintaining thesuperheat;

e) moving the liquid steel into an atomization chamber from the tundishfor atomization with an inert gas, wherein metal powder obtained isdeposited at a bottom of the atomization chamber; then entering a powderstorage with a protective atmosphere; after atomization, screening witha protective screening device before storing in the powder storage; and

f) loading the metal powder in the powder storage into a hot isostaticpressing capsule with inert gas protection; after fully vibrationfilled, evacuate-degassing the hot isostatic pressing capsule; and thensealing welding a capsuling end; finally providing a hot isostaticpressing treatment, in such a manner that the metal powder is fullyconsolidated, and completing powder metallurgy.

The above powder metallurgy comprises non-vacuum melting atomization andhot isostatic pressing processes with full-process protection to controlthe oxygen content and carbide morphology, and optimize an alloyperformance. The covering slag of the ladle is able to cut off the airand conductively heat. The inert gas is injected into the bottom of theladle through the hole, so that temperatures at different positions ofthe liquid steel equals to each other, and harmful inclusions rapidlyfloats, thus being removed. The guiding tube at the bottom of the ladleguides the liquid steel as well as reduces turbulence fluid generatedduring flowing, so as to keep slag and inclusion out. Furthermore, theguiding tube prevents the liquid steel from being exposed to air,avoiding increase of an oxygen content of the liquid steel. The coveringslag of the tundish prevents the liquid steel from being exposed to airwhen the liquid steel flows through the tundish, avoiding increase ofthe oxygen content. The tundish is pre-heated before the liquid steelenters, so as to avoid local condensation or early precipitation of asecond phase when the liquid steel enters into the tundish. The powderstorage has the protection atmosphere inside and a forced coolingfunction. The protective screening device protects a screening processand prevents the powder from flying. The powder storage is connected tothe hot isostatic pressuring capsule in a sealed form, and the inert gasis injected into the hot isostatic pressing capsule before loadingpowder for discharging air, so as to control the oxygen content.

In summary, according to the present invention, a powder metallurgy toolsteel with high wear resistance and high corrosion resistance isobtained, which has an excellent overall performance, especially in thewear resistance and the corrosion resistance, so as to be used underwearing and corroding working conditions. According to the embodimentsof the present invention, the alloy adapts certain chemical componentsand rapid cooling-consolidation process of the powder metallurgy,wherein a type of the MX carbide is (V, Nb) (C, N), in such a mannerthat the MX carbide precipitated is finer and a distribution is evener.With a higher carbide content, it is easy to obtain high toughness andgrinding performance. After heat treatment, the hardness is more thanHRC60, so as to satisfy different application requirements with a widerange of uses. The alloy of the present invention is prepared accordingto the powder metallurgy, wherein a plurality of effective protectionmethods are used for keeping the liquid steel and the powder clean. Anincrease of the oxygen content is ≤30 ppm, which ensures ahigh-performance alloy.

For better understanding by the skilled person in the art, preferredembodiments of the present invention are illustrated as follows.

Preferred Embodiment 1

The preferred embodiment 1 refers to a group of powder metallurgy wearand corrosion resistance alloys, whose chemical components are listed inTable 1.1:

TABLE 1.1 chemical components of powder metallurgy wear and corrosionresistance alloys in the preferred embodiment 1 C W Mo Cr V Nb Co Si MnN S O embodiment 2.68 0.50 1.30 16.50 8.30 2.00 0.20 0.60 0.30 0.12 0.010.006 1.1 embodiment 2.84 0.30 1.30 15.00 9.40 1.80 0.20 0.60 0.30 0.100.01 0.006 1.2 embodiment 3.18 0.82 1.70 14.20 12.00 1.30 0.50 0.80 0.800.30 0.008 0.007 1.3 embodiment 2.45 0.20 1.50 13.40 10.85 0.65 0.300.50 0.50 0.22 0.007 0.008 1.4

The powder metallurgy wear and corrosion resistance alloys are preparedwith a method comprising steps of:

a) loading liquid tool steal of the present invention into a smeltingladle with a load weight of 1.5-8 ton;

b) electrically heating covering slag at a top surface of the liquidsteel in the smelting ladle by graphite electrodes, injecting argon ornitrogen gas from a hole at a bottom of the smelting ladle for stirringthe liquid steel, opening a guiding tube when a liquid steel overheatedtemperature is 100° C.-150° C.;

c) moving the liquid steel into a tundish, which is pre-heated to 800°C.-1200° C., through the guiding tube at the bottom of the smeltingladle, controlling a size of an inlet of the guiding tube, in such amanner that a flow rate of the liquid steel is 10 kg/min-50 kg/min,adding a covering slag when the liquid steel enters into the tundish andburies a bottom end face of the guiding tube;

d) forming powder by atomization while continuously heating the tundishfor maintaining the liquid steel temperature at 100° C.-150° C.;

e) moving the liquid steel into an atomization chamber through anopening at a bottom of the tundish, opening an atomizing gas nozzle,using nitrogen as an atomizing gas for atomization, wherein a nitrogenpurity is ≥99.999%, an oxygen content is ≤2 ppm, a gas pressure is 1.0MPa-5.0 MPa; cracking the liquid steel into drops by impact of an inertgas, while rapidly cooling into metal powder and depositing at a bottomof the atomization chamber; then entering a powder storage through thebottom of the atomization chamber; after atomization, waiting until thepowder in the powder storage is cooled to a room temperature, andscreening with a protective screening device; wherein an inertprotective gas with a positive pressure is injected into a screeningdevice chamber, and the powder storage has a protective atmosphere witha positive pressure inert gas; and

f) loading the metal powder in the powder storage into a hot isostaticpressing capsule, firstly injecting an inert gas into the hot isostaticpressing capsule for excluding air, then connecting the hot isostaticpressuring capsule and the powder storage in a sealed form; providing avibration operation during loading for increasing filling density of themetal powder; then evacuate-degassing the hot isostatic pressing capsulewhile keeping a temperature at 200° C.-600° C.; degassing to 0.01 Pa andcontinuously heating for ≥2 h, and then sealing welding a capsuling end;finally providing a hot isostatic pressing treatment, with a temperatureof 1100° C.-1160° C., and keeping a pressure of ≥100 MPa for ≥1 h,naturally cooling after the metal powder is fully consolidated.

According to requirements, the alloy of the present invention arefurther forged for obtaining certain shapes and sizes, and are treatedwith different heat treatments for obtaining different performances,wherein the heat treatments comprises annealing, quenching andtempering. Annealing comprises steps of heating a forging piece to 860°C.-900° C. and keeping the temperature for 2 h; cooling to 530° C. witha rate of ≤15° C./h; then cooling to below 50° C. by furnace cooling orstatic air cooling. Quenching comprises steps of pre-heating the forgingpiece after annealing at a temperature at 815° C.-845° C.; keeping thetemperature at 1000° C.-1200° C. for 15-40 min after the temperature iseven, then quenching to 530° C.-550° C., and cooling to below 50° C.Tempering comprises steps of heating the forging piece after quenchingto 540° C.-670° C. and keeping the temperature for 1.5-2 h, thenair-cooling to below 50° C.; repeating for 2-3 times.

According to embodiments 1.1-1.4, the powder metallurgy wear andcorrosion resistance alloys are obtained, wherein increase of the oxygencontent during process is ≤30 ppm. After hot working, a fully densealloy with a relative density of 100% is obtained, which is preparedinto columns with a diameter of 50 mm.

Preferred Embodiment 2

The preferred embodiment 2 proves carbide content and particle size,heat treatment hardness, wear resistance, and corrosion resistance ofthe powder metallurgy wear and corrosion resistance alloy of thepreferred embodiment 1, wherein the carbide content and the particlesize is analyzed based on structure images obtained by scanning electronmicroscope; and the heat treatment hardness and the wear resistance aretested referring to GB/T 230.1, and GB/T 12444-2006. The corrosionresistance is tested by immersing in a corrosive agent of 5% HNO₃+1% HClat a room temperature.

The powder metallurgy wear and corrosion resistance alloys of theembodiments 1.1 and 1.2 are compared with a forged tool steel (alloy A)and a powder metallurgy tool steel (alloy B) bought, wherein results areas follows:

TABLE 2.1 components comparison between embodiment 1.1, embodiment 1.2,alloy A, and alloy B C W Mo Cr V Nb Co Si Mn N S O embodiment 2.68 0.501.30 16.50 8.30 2.00 0.20 0.60 0.30 0.12 0.01 0.006 1.1 embodiment 2.840.30 1.30 15.00 9.40 1.80 0.20 0.60 0.30 0.10 0.01 0.006 1.2 A 1.50 00.90 12.05 0.80 0 N.A 0.30 0.35 N.A 0.01 0.005 B 0.80 0 1.30 7.50 2.75 0N.A 0.95 0.70 N.A 0.01 0.008 Referring to Table 2.1, N.A. means notanalyzed.

According to the powder metallurgy wear and corrosion resistance alloysof the embodiments 1.1 and 1.2, the oxygen content is 50-60 ppm beforepreparing and 60-80 ppm after preparing, which means the increase of theoxygen content is ≤30 ppm.

TABLE 2.2 carbide content and particle size comparison betweenembodiment 1.1, embodiment 1.2, alloy A, and alloy B MX carbide M₇C₃carbide quenching tempering volume particle size volume particle sizemethod method vol % μm vol % μm embodiment 1100° C. for 540° C. × 12-20≤1.3 12-19 ≤5 1.1 15 min 1.5 h × 2 embodiment 1100° C. for 540° C. ×12-20 ≤1.3 12-19 ≤5 1.2 15 min 1.5 h × 2 A 1000° C. for 200° C. × 0 012-16 5-30 15 min 1.5 h × 2 B 1100° C. for 540° C. 3-6 0.5-1.5 0 0 15min 1.5 h × 2 Referring to Table 2.2, the carbide particle size refersto a size of carbide with at least 80% of volume content.

According to carbide analysis of the powder metallurgy wear andcorrosion resistance alloy, carbide components are the MX carbide andthe M₇C₃ carbide. The type of the MX carbide is (V, Nb) (C, N), which ismainly formed by V, Nb, C, N and a few alloy elements such as Fe and Cr.The M₇C₃ carbide is a Cr-enriched carbide. According to Table 2.2, theMX carbide of the alloy of the present invention is extremely small,wherein a size of at least 80% of the MX carbide is no more than 1.3 μm.After further measurement, a maximum size of the MX carbide is no morethan 5 μm. Due to a high hardness of the MX carbide, the alloy of thepresent invention is excellent in grinding performance and toughness iseasy to increase. The volume fraction of the MX carbide is up to12%-20%, so as to provide excellent wear resistance. According to thepresent invention, a volume fraction of the M₇C₃ carbide is 12%-19%. Asize of at least 80% of the M₇C₃ carbide is no more than 5 μm judgingfrom volume percentage, and a maximum size of the MX carbide is no morethan 10 μm. The M₇C₃ carbide is bigger than the MX carbide in particlesize, but still smaller than M₇C₃ carbide in the forged alloy A. Thealloy B adapts a powder metallurgy method, wherein carbide particle sizethereof is extremely small. Most MX carbide of the alloy B is 0.5-1.5 μmwith a volume fraction of 3%-6%.

TABLE 2.3 heat treatment hardness and wear resistance comparison betweenembodiment 1.1, embodiment 1.2, alloy A, and alloy B alloy quenchingtempering hardness mass loss method method HRC (mg) embodiment 1100° C.for 540° C. × 1.5 h × 2 61 43 1.1 15 min embodiment 1100° C. for 540° C.× 1.5 h × 2 61 29 1.2 15 min A 1000° C. for 200° C. × 1.5 h × 2 61 27015 min B 1100° C. for 540° C. × 1.5 h × 2 61 174 15 min

According to Table 2.3, after heat treatment, the alloy hardness is morethan HRC60, so as to satisfy application requirements of the alloyaccording to the present invention. Accordingly, wear resistance of thealloy of the present invention is the best.

The corrosion resistance is tested by immersing the alloy of the presentinvention in the corrosive agent of 5% HNO₃+1% HCl at the roomtemperature. The alloy A with a high content of Cr is tested as acontrast, wherein corrosion resistance comparison results are listed inTable 2.4.

TABLE 2.4 corrosion resistance comparison between embodiment 1.1,embodiment 1.2, and alloy A quenching tempering corrosion rate methodmethod (mm/y) embodiment 1.1 1100° C. for 350° C. × 1.5 h × 2 ≤160 15min embodiment 1.2 1100° C. for 350° C. × 1.5 h × 2 ≤160 15 min A 1000°C. for 200° C. × 1.5 h × 2 ≥400 15 min Referring to Table 2.4, the alloyof the present invention is better in corrosion resistance.

It should be noticed that different applications requires different wearand corrosion resistances, so proper heat treatment should be selected.That is to say, with the same quenching conditions, lower tempering willdissolve more Cr in the matrix, so as to obtain higher corrosionresistance. Higher tempering will precipitate more Cr in a carbide form,so as to obtain lower corrosion resistance but higher wear resistance.In general, within a wide heat treatment range, the alloy of the presentinvention is excellent in both wear and corrosion resistances, so as tosatisfy application requirements under wearing and corroding occasions.

In summary, according to the present invention, a powder metallurgy wearand corrosion resistance alloy is obtained, which has an excellentoverall performance, especially with both high wear resistance and highcorrosion resistance, so as to be used under wearing and corrodingworking conditions. According to the present, the alloy adapts certainchemical components and powder metallurgy. With a higher carbidecontent, the carbide particles are still fine and even-distributed,which is conducive to obtain high toughness and grinding performance.After heat treatment, the hardness is more than HRC60, so as to satisfydifferent application requirements with a wide range of uses. Forexample, the present invention is applicable to squeezing plasticmachinery parts such as screws, screw sleeves, screw head as well ascheck rings, and food industry, surgical instruments, industrial cuttingblades, wear and corrosion resistant parts, etc. According to thepresent invention, a plurality of effective protection methods are usedfor keeping the liquid steel and the powder clean. The increase of theoxygen content is ≤30 ppm, which ensures a high-performance alloy.

During description, words such as “first” and “second” are describingonly without indicating importance or numbers of technical features.Therefore, “first” or “second” may refer to one or more features. Duringdescription, “a plurality of” refers to no less than two except fordetailed illustration.

During description, references such as “one embodiment”, “someembodiments”, “an example”, “specific example”, or “some examples” meanthat a particular feature, structure, material, or characteristic of thedescribed embodiments or examples are included in at least oneembodiment or example of the present invention. In the specification,the terms of the above schematic representation is not necessarily forthe same embodiment or example. Furthermore, the particular features,structures, materials, or characteristics described in any one or moreof the embodiments or examples are able to be combined in a suitablemanner. One skilled in the art will understand that features indifferent embodiments or examples may be combined if not conflicting toeach other.

One skilled in the art will understand that the embodiment of thepresent invention as shown in the drawings and described above isexemplary only and not intended to be limiting. It will thus be seenthat the objects of the present invention have been fully andeffectively accomplished. Its embodiments have been shown and describedfor the purposes of illustrating the functional and structuralprinciples of the present invention and is subject to change withoutdeparture from such principles. Therefore, this invention includes allmodifications encompassed within the spirit and scope of the followingclaims.

1-13. (canceled)
 14. A powder metallurgy wear and corrosion resistancealloy, comprising chemical components by mass percent of: C:2.36%-3.30%, W: 0.1%-1.0%, Mo: ≤1.8%, Cr: 12.6%-18.0%, V: 6.0%-12.5%,Nb: 0.5%-2.1%, Co: 0.1%-0.5%, Si: ≤1.0%, Mn: 0.2%-1.0%, N: 0.05%-0.35%,with balance iron and impurities; wherein a carbide component of thepowder metallurgy wear and corrosion resistance alloy is an MX carbideand a M₇C₃ carbide, wherein the MX carbide has a NaCl type face-centeredcubic lattice structure; an M element of the MX carbide comprises V andNb, and an X element comprises C and N.
 15. The powder metallurgy wearand corrosion resistance alloy, as recited in claim 14, wherein theimpurities comprise O, wherein an O content is no more than 0.01%. 16.The powder metallurgy wear and corrosion resistance alloy, as recited inclaim 14, comprising the chemical components by mass percent of: C:2.40%-3.18%, W: 0.1%-0.8%, Mo: ≤1.8%, Cr: 13.0%-18.0%, V: 6.2%-12.5%,Nb: 1.0%-2.0%, Co: 0.1%-0.4%, Si: ≤0.8%, Mn: 0.2%-0.8%, N: 0.05%-0.30%,O: ≤0.008%, with balance iron and impurities.
 17. The powder metallurgywear and corrosion resistance alloy, as recited in claim 15, comprisingthe chemical components by mass percent of: C: 2.40%-3.18%, W:0.1%-0.8%, Mo: ≤1.8%, Cr: 13.0%-18.0%, V: 6.2%-12.5%, Nb: 1.0%-2.0%, Co:0.1%-0.4%, Si: ≤0.8%, Mn: 0.2%-0.8%, N: 0.05%-0.30%, O: ≤0.008%, withbalance iron and impurities.
 18. The powder metallurgy wear andcorrosion resistance alloy, as recited in claim 14, wherein theimpurities comprise S, wherein a S content is no more than 0.1%.
 19. Thepowder metallurgy wear and corrosion resistance alloy, as recited inclaim 17, wherein the impurities comprise S, wherein a S content is nomore than 0.1%.
 20. The powder metallurgy wear and corrosion resistancealloy, as recited in claim 14, wherein the impurities comprise P,wherein a P content is no more than 0.03%.
 21. The powder metallurgywear and corrosion resistance alloy, as recited in claim 19, wherein theimpurities comprise P, wherein a P content is no more than 0.03%. 22.The powder metallurgy wear and corrosion resistance alloy, as recited inclaim 14, wherein a volume fraction of the MX carbide is 12%-20%. 23.The powder metallurgy wear and corrosion resistance alloy, as recited inclaim 21, wherein a volume fraction of the MX carbide is 12%-20%. 24.The powder metallurgy wear and corrosion resistance alloy, as recited inclaim 14, wherein a size of at least 80% of the MX carbide is no morethan 1.3 μm judging from volume percentage.
 25. The powder metallurgywear and corrosion resistance alloy, as recited in claim 23, wherein asize of at least 80% of the MX carbide is no more than 1.3 μm judgingfrom volume percentage.
 26. The powder metallurgy wear and corrosionresistance alloy, as recited in claim 25, wherein a maximum size of theMX carbide is no more than 5 μm.
 27. The powder metallurgy wear andcorrosion resistance alloy, as recited in claim 14, wherein the M₇C₃carbide is a Cr-enriched carbide.
 28. The powder metallurgy wear andcorrosion resistance alloy, as recited in claim 26, wherein the M₇C₃carbide is a Cr-enriched carbide.
 29. The powder metallurgy wear andcorrosion resistance alloy, as recited in claim 14, wherein a volumefraction of the M₇C₃ carbide is 12%-19%.
 30. The powder metallurgy wearand corrosion resistance alloy, as recited in claim 28, wherein a volumefraction of the M₇C₃ carbide is 12%-19%.
 31. The powder metallurgy wearand corrosion resistance alloy, as recited in claim 30, wherein a sizeof at least 80% of the M₇C₃ carbide is no more than 5 μm judging fromvolume percentage.
 32. The powder metallurgy wear and corrosionresistance alloy, as recited in claim 31, wherein a maximum size of theMX carbide is no more than 10 μm.
 33. The powder metallurgy wear andcorrosion resistance alloy, as recited in claim 32, wherein the M₇C₃carbide has a hexagonal lattice structure.